
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>复选框（checkbox）全选/全不选/返选</title>
<style>
body,dl,dt,dd,p{margin:0;padding:0;}
body{font-family:Tahoma;font-size:12px;}
label,input,a{vertical-align:middle;}
label{padding:0 10px 0 5px;}
a{color:#09f;text-decoration:none;}
    
a:hover{color:red;}
dl{width:120px;margin:10px auto;padding:10px 5px;border:1px solid #666;border-radius:5px;background:#fafafa;}
dt{padding-bottom:10px;border-bottom:1px solid #666;}
dt label{font-weight:700;}
p{margin-top:10px;}
</style>
<script type="text/javascript">
window.onload = function ()
{
	var oA = document.getElementsByTagName("a")[0];	
	var oInput = document.getElementsByTagName("input");
	var oLabel = document.getElementsByTagName("label")[0];
    /* 部分选择 */
	var isCheckAll = function ()
	{
		for (var i = 1, n = 0; i < oInput.length; i++)
		{
			oInput[i].checked && n++	/*判断句：当oInput.checked为true，n计数。否则，n === 0；*/
            console.log(n);
		}  
        console.log(n) /*记录当前所有oInput.checked为true的数量*/
		oInput[0].checked = n == oInput.length - 1; /*判断是否为最后一个oInput*/
		oLabel.innerHTML = oInput[0].checked ? "全不选" : "全选"
	};
	//全选/全不选
	oInput[0].onclick = function ()
	{
		for (var i = 1; i < oInput.length; i++)
		{
			oInput[i].checked = this.checked			
		}
		isCheckAll()
	};
	//反选
	oA.onclick = function ()
	{
		for (var i = 1; i < oInput.length; i++)
		{
			oInput[i].checked = !oInput[i].checked
		}
		isCheckAll()
	};
	//根据复选个数更新全选框状态
	for (var i = 1; i < oInput.length; i++)
	{
		oInput[i].onclick = function ()
		{
			isCheckAll()
		}	
	}	
}
</script>
</head>
<body>
<dl>
    <dt><input type="checkbox" id="checkAll" /><label>全选</label><a href="javascript:;">反选</a></dt>
    <dd>
        <p><input type="checkbox" name="item" /><label>选项（一）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（二）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（三）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（四）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（五）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（六）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（七）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（八）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（九）</label></p>
        <p><input type="checkbox" name="item" /><label>选项（十）</label></p>
    </dd>    
</dl>
<center>1、切换全选/全不选文字；2、根据选中个数更新全选框状态；</center>
</body>
</html>
